The present invention relates to a method of forming by projection an integrated circuit pattern on a semiconductor wafer and, more particularly, to a method of forming an integrated circuit pattern on a semiconductor wafer by irradiating it with a radiant beam which passes through a projecting mask for forming the integrated circuit pattern.
To manufacture a semiconductor integrated circuit, it is necessary to repeatedly form various integrated circuit patterns on a semiconductor wafer. A method of preforming a semiconductor integrated circuit pattern on a mask, of collectively projecting such a pattern onto the semiconductor wafer by the use of an optical projection technique and of exposing the same has hitherto been widely used. Since a large number of figures can be collectively formed using projection, it has the merit of being highly efficient.
Integrated circuits have recently become increasingly complex, as well as increasingly minute or fine. To further increase the degree of integration, therefore, it is necessary to form patterns with a higher precision. For example, when an integrated circuit pattern having a wire diameter of one to two microns is formed, a reduction projection aligner, or a reduction transfer apparatus is used to reduce the size of the pattern on a mask and to project the same onto a semiconductor wafer. This apparatus, indeed, makes it possible to form a pattern with a higher precision than that obtainable with a prior art projector apparatus having a projection ratio 1:1. However, this apparatus is expensive and small in through-put thus making the cost of pattern formation high. Because of this, a technique combining projector apparata to form patterns on the same semiconductor wafer is contemplated as a method of forming a highly precise pattern more cheaply.
However, whether or not one projector apparatus is interchangeable with another becomes an important question. Usually, each projector apparatus has its own level of distortion. Accordingly, when a pattern is projected on a wafer by a second projector apparatus, even more distortion or displacement occurs, resulting in decreased pattern precision. In order to solve this problem, it is necessary to remove the characteristic of projection distortion from each apparatus. Unfortunately, it is almost impossible to design a projector apparatus without any projection distortions. Therefore, two or more projector apparata are used only in combination when the distortion of patterns due to superposition falls within a permissible range. This greatly limits improving pattern formation efficiency.